Internal compiler error: unexpected panic

[gibsond]

Hello,

I apologize up front if I am raising this issue incorrectly. The compiler says it would appreciate a bug report. Below is what it printed out:

hread 'main' panicked at 'cannot access a scoped thread local variable without calling `set` first', /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:186:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.29.2 (17a9dc751 2018-10-05) running on x86_64-unknown-linux-gnu
note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin
note: some of the compiler flags provided by cargo are hidden
error: Could not compile `state2_test`.
To learn more, run the command again with --verbose.

---

It happened, for the first time, when declaring a reference in a function:

let ref tok_prediction:HashSet<u16>;

and then assigning it in each branch of an if condition:
if is_data {
tok_prediction = &self.data_predictions;
} else {
tok_prediction = &self.next_cwa.1;
}
if tok_prediction.contains(&cwa) {

};

It does not always fail on a cargo build, but generally will fail after a cargo clean, cargo build.
It generally always fails on a cargo build --release.

Let me know if this issue report is acceptable,
Daniel Gibson

[ExpHP]

I deleted some of my earlier replies which were incorrect. As the OP reports, the issue is transient and difficult to reproduce. I noticed that the ICE occurs on the playground in stable yet not in beta or nightly... but then when I tried on my local machine, compilers from all three channels handle it fine.

(note: one of the deleted posts asked the OP to try the beta compiler)

Here is a backtrace procured from the playground.

thread 'main' panicked at 'cannot access a scoped thread local variable without calling `set` first', /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:186:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:479
   6: std::panicking::begin_panic
   7: <scoped_tls::ScopedKey<T>>::with
   8: syntax_pos::<impl syntax_pos::span_encoding::Span>::macro_backtrace
   9: rustc_errors::emitter::EmitterWriter::fix_multispan_in_std_macros
  10: <rustc_errors::emitter::EmitterWriter as rustc_errors::emitter::Emitter>::emit
  11: rustc_errors::Handler::emit_db
  12: <rustc_errors::Handler as core::ops::drop::Drop>::drop
  13: core::ptr::drop_in_place
  14: core::ptr::drop_in_place
  15: core::ptr::drop_in_place
  16: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  17: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  18: rustc_driver::run
  19: rustc_driver::main
  20: std::rt::lang_start::{{closure}}
  21: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  22: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  23: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  24: main
  25: __libc_start_main
  26: <unknown>
query stack during panic:
end of query stack

[ExpHP]

Hmmm, maybe this WAS fixed: #53469 (seemingly completely different issue, but look at the error and backtrace)

[gibsond]

As requested, I tried it with +beta and so far I have not been able to reproduce the problem.

Daniel Gibson

[gibsond]

Appears fixed on rustc 1.30.0